A change of plans: Errol, the new GSP mission

Update: The charge controller arrived shortly after i published this article, so i adapted the mission slightly (again), and i will use solar power and the bigger test panel after all. This also means i will run the mission for longer.

Overview

I'm still waiting for parts for the planned missions. But i'm tired of waiting. So i'm changing the plans for future missions. T-REx and Soprano in their current definition are canceled.

I can't even start software development properly, until i know exactly which hardware i have on the mission. For example, the telemetry frames would be optimized to transmit a number of sensors. Until i know which sensor i have, i can't finalize the telemetry design. For example, i don't have my new voltage and amperage sensors yet. My best guess is that they are still on a container ship, awaiting transit through the Suez canal.

Another thing is, after much research, i finally settled on a solar charger and battery design. It will be a 6 Volt system with a lead acid battery. Mostly, because they are cheap, have a good power-to-weight ratio and don't mind harsh temperatures (high and low) as much as other systems. Of course, i already recieved the battery and the solar cells, but the charge controller is still "in transit". Edit: charge controller has arrived.

So, i'm designing a new mission around what i have available.

New mission: Errol

Early reduced reseach of outdoor light is an early Scotty class mission, named after a Discworld swamp dragon. It's main goal is to test my basic design of solar panels, while still beeing powered by batteries. The small test panels will probably not be powerful enough to run the mission hardware during the day, but i might try anyway. Edit: With the charge controller arriving unexpectedly, Errol will be solar powered after all.

Another goal is to run much longer on batteries than FAST CORE did. For this, i'm testing the newly designed power manager that only uses a few milliwatts in standby.

Mission objectives

Required

These are the objectives that must the fulfilled. If anyone of these don't work, it's a mission failure.

Use the same computer hardware (Arduino Mega 2560 R3) as planned for future Tombaugh class missions

Use the same basic design for the power controller (Arduino Mini) as planned for future Tombaugh class missions

Use the same communication hardware as all currently planned future missions (NRF24L01+)

Power manager

Main computer

The main computer now gets his power from the power manager via the the new 7 pin connector cable, which also carries Serial, Power-Hold, Powermanager-Reset (more on that in later article).

(Very) keen eyes might also notice that i upgraded from a DHT11 temperature and humidity sensor to a DHT22. I needed a few new ones anyway, and the DHT22 seem to be more precise for pretty much the same price.

Solar test panels

A bit of good old fashioned bodging with spare bits of wood and lots of glue and duct tape gave me some astonishingly sturdy frames for my solar panels. This should be good enough for the few weeks (or months) this is going to be used. And more importantly, all could be done indoors without noxious paint fumes (it's freezing outside).

Then i went on to solder the solar cells. This isn't as easy as popular Youtubers make it look. Ok, they might not be as clumsy as me, but still i'm glad i didn't make the big one i planned at first. Making the two small panels taught me some good lessons, while risking only a few of the cells.

The 1.89 volts seen here are generated from the LED lamps on the ceiling. Should be much higher with real sunlight.

There is still the small matter of protecting them with a layer of Epoxy resin, which will have to wait for non-freezing conditions outside, which i hope will happen in the next few days. I'm not sure how much i will loose after i pour some (hopefully) transparent resin on top.

In theory, these should max out at 1.2 Amps at 4 Volts when run in series like i did here (so about 4.8 Watts). If i manage to get 300 milliamps at 3 Volts or so (0.9 Watts) this should be enough to run the probe on solar alone. In theory, at least.